Machine for driving mine roof pins having coaxial jacking means

ABSTRACT

This pin driving machine includes a pin-engaging piston, which moves the pin out of a cylinder and into the mine roof when the machine is positioned between a mine roof and a mine floor. The machine includes a roof-engaging pressure plate and block at one end carried by the pin cylinder, and a floor-engaging base at the other end supporting a coaxial, hydraulic jack assembly, which is telescopically related to the pin cylinder. The pin cylinder and the pressure plate are moved into the incipient pin driving position by the coaxial hydraulic jack assembly, which includes a jack cylinder receiving the pin cylinder therein and a valve, controlling hydraulic pressure in the two cylinders incident to extension and retraction of the pin-engaging piston.

United States Patent 1 Elders et al.

[4 1 Feb. 4, 1975 MACHINE FOR DRIVING MINE ROOF PINS HAVING COAXIAL JACKING MEANS [76] Inventors: Gerald W. Elders, P.O. Box 1369,

Aspen, Colo. 81611; Thomas R. Alongi, 350 E. Main St., DuQuoin, Ill. 62832; Thomas E. Schneider, deceased, late of 601 E. Park St., Duquoin, [11. 62832; Thomas R. Schneider, administrator, 527 Mallory Ln., Duquoin, Ill. 62832 22 Filed: Jan.4, 1974 21 Appl. No.: 430,639

Related US. Application Data [63] Continuation-in-part of Ser. No. 202,611, Nov. 26, 1971, Pat. No. 3,819, 101, which is a division of Ser. No. 846,795, Aug. 1, 1969, abandoned.

[52] US Cl 227/130, 227/140, 227/156,

29/252, 254/29, 61/45 B [51] Int. Cl B27f 7/02 [58] Field of Search 227/124, 130, 140, 156;

29/252; 254/29 R, 29 A; 61/45 B, 63; 173/31, 34, 35, 36; 92/161; 91/153, 159, 173

[56] References Cited UNITED STATES PATENTS 2,395,123 2/1946 l-lutt 227/l30 X 2,900,637 8/1959 Schofroth 227/130 X Primary ExaminerGranville Y. Custer, Jr.

[57] ABSTRACT This pin driving machine includes a pin-engaging piston, which moves the pin out of a cylinder and into the mine roof when the machine is positioned between a mine roof and a mine floor. The machine includes a roof-engaging pressure plate and block at one end carried by the pin cylinder, and a floor-engaging base at the other end supporting a coaxial, hydraulic jack assembly, which is telescopically related to the pin cylinder. The pin cylinder and the pressure plate are moved into the incipient pin driving position by the coaxial hydraulic jack assembly, which includes a jack cylinder receiving the pin cylinder therein and a valve, controlling hydraulic pressure in the two cylinders incident to extension and retraction of the pin-engaging piston.

12 Claims, 3 Drawing Figures PATENTED FEB 41375 SHEET 2 [1F 2 FIG.

l MACHINE FOR DRIVING MINE ROOF PINS HAVING COAXIAL JACKING MEANS CROSS REFERENCE TO RELATED APPLICATIONS:

.This application is a continuation-in-part of copending application Ser. No. 202,61], filed Nov. 26, I97], and now U.S. Pat. No. 3,8l9,ll, which is a division of Ser. No. 846,795, filed Aug. 1, I969 now abandoned.

Application Ser. No. 202,097, filed Nov. 26, l97l, and now U.S. Pat. No. 3,72I,094, is a continuation of application Ser. No. 846,795, filed Aug. 1, I969 now abandoned; and application Ser. No. 186,848, filed Oct. 6, 1971 and now Pat. No. 3,734,380, is a continuation-in-part of application Ser. No. 846,795, filed Aug. 1, 1969 and now abandoned.

SUMMARY OF THE INVENTION This invention relates generally to a machine for driving mine roof pins and more particularly to an improved jacking means for such a machine.

U.S. Pat. No. 3,734,380 issued to the inventors named herein discloses a machine for driving mine roof pins by which a pin is pressed into a mine roof by a substantially smooth pushing force that avoids shock disturbance of roof material and eliminates the need for drilling holes. The driving of the pin is achieved by means of hydraulic piston and cylinder assembly in which the pin is received by the cylinder and, when the machine is positioned in the desired location, is, driven by the piston into the roof strata. The mine roof pins are relatively long and slender and the machine provides a unique pin-centering support system to avoid buckling of the pin during the driving process. The pincentering support extends along the cylinder and is carried by the piston so as to move with the piston when the piston drives the pin out of the cylinder and into a mine roof. The pin-centering support engages the pin to guide and support the pin during driving, and moves laterally out of the cylinder as it disengages that portion of the pin about to enter the mine roof. A receiving assembly is provided which guides and receives the pincentering support after it moves laterally out of the pin cylinder.

The machine described in U.S. Pat. No. 3,734,380 is placed in the incipient pin driving condition by a hydraulic jacking assembly, having a base at one end and a roof-engaging pressure plate at the other end, which, in effect, provides a means of expanding the machine between the mine roof and the subjacent floor so that it is secured in place prior to the actual driving of the pin. The particular jacking system disclosed in this patent comprises a pair of jacks located at opposite sides of, and strapped to the pin cylinder. This system is structurally and hydraulically complicated and is a cumbersome arrangement which renders the machine as a whole unwieldy, and therefore relatively difficult to position and operate.

The present jacking system overcomes these disadvantages in a manner not disclosed in the known prior art.

SUMMARY OF THE INVENTION This pin driving machine is similar to that described in U.S. Pat. No. 3,734,380 in so far as it provides a hydraulic piston and cylinder assembly, in which a pin is received by the cylinder and driven by the piston with a smooth pushing force into the roof strata, and a pin centering support is provided to support the pin during driving. A hydraulic .jacking means is provided to expand the machine between the mine roof and the mine floor and place the machine in an incipient pin driving condition. The structural arrangement of parts of the jacking means, and the cooperation between said jacking means and the other primary elements of the machine are completely different from those described in U.S. Pat. No. 3,734,380. importantly, the jacking means, which cooperates with the pin cylinder to place the machine in an incipient pin driving condition, is coaxially related to the pin cylinder and provides a jack cylinder which receives the pin cylinder in telescopic relation so that the pin cylinder, in effect, provides the piston of the jack cylinder.

The jacking means is relatively easy to construct and inexpensive to manufacture and is relatively simple to operate.

It is an object of this invention to provide a pin cylinder carrying a pressure plate, engageable with the mine roof, the pin cylinder having a pin driving piston movably received therein, and to provide a coaxial jacking means for urging the pin cylinder and the pressure plate toward the mine roof to place the machine in an incipient, pin driving condition.

Another object is to provide a jacking means having a jack cylinder and a jack piston, the jack piston being integral with the pin cylinder so that the pin cylinder is telescopically received within the jack cylinder.

Still another object is to provide a pin cylinder and a jack cylinder which cooperate to define a first pressure chamber, whereby fluid supplied to said chamber urges the pin cylinderand the-pressure plate into engagement with the mine roof; and to provide a pin piston and a pin cylinder which cooperate to define a second pressure chamber, whereby fluid supplied to said chamber urges the pin piston toward said mine roof to drive said pin into the roof strata.

It is an object to provide valve-controlled passage means communicating between said first and second chambers to permit fluid flow therebetween, when the pressure in the first chamber reaches a predetermined value, incident to the urging of the pin piston toward the mine roof.

Another object is to provide a valve which controls fluid flow from said second chamber to said first chamber, when the pressure in the second chamber reaches a predetermined value, incident to retraction of the pin piston into the pin cylinder.

It is another object to provide a valve block between the pin cylinder and the jack cylinder which houses the valve and provides the first chamber with an annular configuration when the pin cylinder is fully retracted.

Yet another object is to provide a pin support means within the pin cylinder including a plurality of pin support lengths attached to the pin piston, which guide the pin upwardly and move laterally out of the pin cylinder on disengaging the pin, and into associated receiving cylinders, said receiving cylinders providing pistons applying a force to said pin piston, through said support lengths, to open the valve incident to retraction of the pin piston.

FIG. 3 is a cross sectional view taken on line 3-3 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT:

Referring now by characters of reference to the drawings and first to FIG. 1 it will be understood that the pin driving machine, generally indicated by 10, is located and extends between a mine roof 11 and a subjacent mine floor 12.

The machine includes an elongate pin cylinder 13, and a positioning means provided by a coaxial hydraulic jack assembly generally indicated by 14, which receives the pin cylinder 13 in telescopic relation. The lower portion of pin cylinder 13 forms a part ofthe jack assembly, and, in effect, provides a jack piston, which is received in sliding relation within a jack cylinder 15.

The machine 10 is shown in a substantially upright, incipientpin driving position in FIG. 1 and includes a base 19 at the lower end, which is seated on the mine floor I2 and supports the jack cylinder 15; and a pressure plate at the upper end, which is carried by the pin cylinder 13. In the incipient pin driving position the jack assembly 14 is extended so that the pin cylinder 13 and the pressure plate 20 are in a raised condition. To effectuate the connection between the pressure plate 20 and the pin cylinder 13, said cylinder is provided with a seating flange 16, attached as by welding to its upper end.' The pressure plate 20 is attached to the seating flange 16 by a connector ring 17, which is attached to the pressure plate 20 by a plurality of post members 18, see FIG. 2, welded between said ring 17 and said plate 20, said connector ring and said post members constituting a bracket means. The connector ring 17, and therefore the pressure plate 20,is connected to the pin cylinder seating flange 16 as by a plurality of stud fasteners 17. A wood block 21 is disposed on top of the pressure plate 20 overlapping the open pin cylinder end 22. Upon extension of the jack assembly 14 to the position shown in FIG. 1 the pressure plate 20 moves upwardly with the pin cylinder 13 and urges the wood block 21 against the mine roof 1] to clamp the block 21 in place at the predetermined roof area location.

A plurality of receiving cylinders 23 depend downwardly from the connector ring 17 in parallel relation with the pin cylinder 13, and are attached, as by welding, to said connector ring 17. As is illustrated in FIG. 2 the receiving cylinders 23 are located circumferentially at equidistant points about the pin cylinder 13. The receiving cylinders 23 are connected to the pin cylinder 13 by means of a circumferential strap 70 attached, as by welding, to the pin cylinder 13 and having a plurality of outstanding lugs 71. Each receiving cylinder 23 includes an arcuate strap 72 attached thereto as by welding, and having an outstanding lug 73 attached to an associated lug 71 by fasteners 74. The structure and function of these receiving cylinders 23 will be explained upon later detailed description of parts.

As shown clearly in FIG. 1 a piston 24 is located and slidably mounted in cylinder 13, the piston 24 including a reduced portion 25 that provides an internal socket 26 adapted to seat and hold the head 27 of an elongate pin 28 that is to be driven into the mine roof 11 by said piston 24.

The pressure plate 20 is provided with a central opening 30 that is aligned with, and located above, the open cylinder end 22, the opening 30 being of sufficient diameter to permit passage of the pin head 27 and the piston portion 25 as the pin is completely driven. The pressure plate 20 includes an annular recess 32, said recess being concentric with the plate opening 30. A bearing disc 33 is adapted to fit into the space provided by the recess 32, and is thereby disposed between the wood block 21 and the pressure plate 20. This bearing disc 33 engages the pin head 27 when the pin 28 is fully driven and is retained by the pin head 27 against the wood block 21.

A pin-centering support means generally indicated by 34 extends along the cylinder 13 and is supported by the piston 24 so as to move with the piston when the piston drives the pin 28 along and out of the cylinder 13 and into the mine roof 11. The pin-centering support means 34 includes a plurality of support lengths (four in the preferred embodiment) extending into the cylinder 13 between the pin 28 and the internal wall 36 of the cylinder 13. Each support length includes a plurality of interengaging, relatively movable support members 37. Each support member 37 includes a pair of laterally spaced integral ears 38 adapted to embrace the projecting lug 40 of the next adjacent support member 37. A pivot pin 41 extends through the overlapping ears 38 and projecting lug 40 to pivotally interconnect the adjacent support members 37. When so connected, the support length 35 constitutes a chain, in which the support members 37 are movable relative to the cylinder 13.

An arcuate bearing surface 43 is located on the inner margin of each support member 37 conforming substantially to the periphery of the pin shank, and anarcuate bearing surface 44 is provided on the outer margin of each support member 37 conforming substantially to the arcuate configuration of the inner cylinder wall 36. It will be understood that when the support members 37 of each support length 35 are aligned within the cylinder 13, the bearing surfaces 43 are in substantial alignment and form a substantially continuous bearing support against the shank of pin 28, while the bearing surfaces 44 engage the cylinder wall 36. Accordingly, the support lengths 35 center and support the pin 28 to preclude any undesirable deformation or buckling of the pin shank as the pin 28 is pushed under tremendous hydraulic pressure into the mine roof.

The end of each support length 35 includes a plurality of end support members 45 that serve to connect the support length to the piston 24. These members 45 are similar to members 37 except that they include inner bearing surfaces 48 adapted to engage the reduced piston portion 25. One of the end support members 45 is pivotally connected to an adjustable threaded element 52 fixed to the top surface of piston 24, while another end support member 45 is pivotally connected to the first of the support members 37 engageable with the pin shank.

A receiving means generally indicated by 53 directs each of the support lengths 35 in a predetermined path as the support length 35 moves laterally out of the cylinder 13. The receiving means includes the cylinder 23 that has an open end 55 into which each support length 35 moves. The pair of laterally spaced plates 56 are secured to the underside of the pressure plate 20 and said plates 56 are provided with internal tracks 57 extending from the open end 22 of the pin cylinder 13 to said open end 55 of the associated receiving cylinder 23. Mounted on opposite ends of each of the pivot pins 41 connecting support members 37 are rotatable bearings 58 that ride in tracks 57. In order for the support members 37 of each support length 35 to provide maximum support for the pin shank, the underside ofthe pressure plate 20 is provided with an arcuate groove 60 into which the support members 37 move as each support length 35 moves laterally out of the pin cylinder.

As shown in FIGS. 1 and 2, and noted above, the receiving cylinders 23 are attached to the connector ring 17. To facilitate this connection the connector ring 17 is provided with a plurality of circumferentially spaced openings 75 having an arcuate configuration to accommodate the cylinders 23 and facilitate welding attachment of said cylinders to the connector ring 17. Because of the connection of the receiving cylinders 23 and the pressure plate 20 to the pin cylinder 13, these members move in unison with said pin cylinder. 1n the preferred embodiment a secondary power means is provided for urging the support lengths 35 back into the pin cylinder 13 incident to retraction of the piston 24. This secondary power means includes a piston 61 reciprocatively mounted within each receiving cylinder 23. A link 62 pivotally interconnects the last support member 37 to an adjustable threaded member 63 fixed to the top surface of piston 61. When the pressure is removed from the underside of piston 24, after the pin 28 has been driven, fluid is admitted through ports 69 into the receiving cylinders 23 and fluid pressure is exerted on the underside of each piston 61, thereby moving the piston 61 upwardly within the receiving cylinders 23, to move the support length 35 back into the pin cylinder 13 and retract the piston 24.

Turning now to the coaxial jack assembly 14 it will be understood that the lower end of the jack cylinder is enlarged to provide a flange 76 having a ball member 77 attached thereto. The base 19 includes a socket portion 78 receiving the ball member 77 and the ball and socket arrangement provides the jack assembly 14 with substantially universal movement relative to the base 19.

As shown clearly in FIG. 1 the pin cylinder 13 is telescopically mounted within the jack cylinder 15. The lower end of the pin cylinder 13 is enlarged to provide an integral piston head 80. The piston head 80 includes a reduced concentric end 81 having transverse passages 82 and 83, which communicate with the interior of the pin cylinder 13 by means of axial passage 84. Passage 82 includes a reduced portion 85, which is closed by means of a check valve 86 and passage 83 includes a reduced portion 87, which is closed by means of a check valve 88.

The jack cylinder 15 is supplied with hydraulic fluid through an inlet port 90 which raises the pin cylinder 13 to the incipient pin driving position at which time the check valve 88 opens to admit fluid into the pin cylinder 13 to urge the pin piston 24 upwardly to drive the pin 28 into the mine roof 11. After the pin 28 has been driven, the pin cylinder 13 is fully retracted and the check valve 86 then opens to discharge fluid from the pin cylinder 13 incident to retraction of the pin piston 24.

The upper end of the jack cylinder 15 includes an annular ring 91, attached thereto as by welding, to which an annular cap 92 is connected as by fasteners 93. The cap is provided with a sealing ring 94 which closes the cylinder end.

it is thought that the operational and functional advantages of the pin driving machine with the coaxial jacking assembly, have become fully apparent from the foregoing description of parts, but for completeness of disclosure the driving operation will be briefly described. I

The machine 10 is located in a substantially upright position, below the point at which a pin 28 is to be driven, in the fully retracted condition of both the pin piston 24 and the jack assembly 14, and with the wood block 21 in position on the pressure plate 20. In this condition, with the base 19 engaging the mine floor 12, the pressure plate 20, with a wood block 21 in place above a bearing disc 33, is somewhat below the position shown in FIG. 1. The lower portion of the pin cylinder 13, designated as piston head 80, is bottomed out, with the reduced concentric end 81 in the position shown in broken outline in FIG. 1 by numeral 81. The piston 24 is located in the lowermost position as shown in FIG. 1. The pin 28 is supported along its length by a plurality of support members 37.

Fluid is admitted into the portion of the jack cylinder 15 below the pin cylinder 13, which portion constitutes a first pressure chamber, to exert pressure against the lower piston head of said pin cylinder 13. This pressure moves the cylinder 13 upwardly, together with the receiving cylinders 23 and the pressure plate 20 which are connected thereto, until the wood block 21 engages the mine roof 1]. Following this engagement the pressure builds up to clamp the wood block 21 between the mine roof 11 and the pressure plate 20 until, at a predetermined pressure, the check valve 88 is opened to admit fluid through the passage 84 into the portion of the cylinder 13 below the piston 24, which portion constitutes a second pressure chamber. This marksthe incipient pin driving condition shown in FIG. 1. Fluid admitted into the pin cylinder 13 exerts a pressure below the piston 24, moving the piston 24 upwardly so that the pin 28 moves through the wood block 21 and penetrates the strata of the mine roof 11. As the pin 28 moves upwardly and is driven under this substantially smooth pushing force into the mine roof 11, the pin is supported at all times by the pin-centering support means 34. More particularly, the support members 37 of each support length 35 move upwardly with the piston 24 so that the bearing surfaces 43 engage the pin periphery with relatively no movement therebetween, while the bearing surfaces 44 slide on the cylinder wall 36. This longitudinal support provided by the support lengths 35 about the periphery of the pin 28 precludes any buckling or deformation of the pin shank as the pin 28 is driven into the mine roof under the force exerted by piston 24.

As the pin 28 is driven, the support members 37 of each support length 35 move laterally outwardly of the pin cylinder 13 in the region just below the pressure plate 20. Upon continued upward movement of the piston 24 the pin 28 is fully driven until the pin head 27 engages the bearing disc 33 on the underside of the wood block 21.

When the pin 28 has been completely driven, the pressure in the jack cylinder is relieved by opening port 90. When the pressure on the underside of the pin cylinder 13 is thus relieved, said pin cylinder 13, together with the pressure plate and receiving cylinders 23, is lowered under gravity. When the cylinder 13 is fully retracted within the jack cylinder 15 so that the valve block 81 bottoms out, the pressure plate 20 is sufficiently spaced from the mine roof 1] so that the machine can be tilted and removed from the location in which the pin has just been driven. At this stage the pin piston 24 is still in the upper portion of the pin cylinder 13 with the end of the piston 24 laterally clear of the pin support lengths 35 and disposed in the pressure plate opening 30. With the machine tilted, a roof pin 28 is inserted through the plate opening 30 so that the pin head 27 is received in the socket 26. By admitting fluid into ports 69 of the receiving cylinders 23 the secon-' dary power means, provided by pistons 61 moving upwardly in their receiving cylinders 23, moves the support lengths outwardly of such cylinders 23 and into the pin cylinder 13, thereby retracting the piston 24 and causing the pin 28 to descend when the pressure from the secondary power means is sufficient to overcome the predetermined pressure required to open the check valve 85 so that fluid is expelled from the cylinder 13 through passage 84 into cylinder 15 and thence through the open port 90. It will be understood that the valve block 81 provides a spacer which results in an annular chamber of finite volume being formed in the bottom of the cylinder 15 when the cylinder 13 is in the fully retracted position.

As the support members 37 of the support lengths 35 move into the pin cylinder 13, the bearing surfaces 43 engage the pin shank and the bearing surfaces 44 engage thecylinder wall 36. It will be understood that the pin 28 is centered by the support lengths 35 and is held in position as the piston 24 moves to its retracted position in the pin cylinder l3.-When the piston 24 is located in this fully retracted position, fluid pressure is relieved from the underside of the piston 61 in the receiving cylinders 23 by opening ports 69. The bearing discs 33 and another wood block 21 are then located in position on top of the pressure plate 20 and the machine is moved into an upright position and to another location for a repetition of the pin driving cycle.

We claim as our invention:

1. In a machine for driving mine roof pins:

a. an elongate pin cylinder,

b. a pin piston movably received in the pin cylinder,

the pin piston providing a seat for a mine roof pin,

c. a pressure plate carried by and movable with the pin cylinder,

d. a base supported by the mine floor, and

e. jacking means supported by the base and urging the pin cylinder and the pressure plate toward the mine roof, said jacking means including a jack piston member and a jack cylinder member coaxial with the pin cylinder, said jack .piston member being integral with said pin cylinder for movement with said pin cylinder and said jack cylinder member being movable relative to said pin cylinder.

2. A machine for driving mine roofpins as defined in claim 1, in which:

f. the jack piston member is telescopically received within the jack cylindermember.

3. A machine for driving mine roof pins as defined in claim 2, in which: j

g. the jack piston member and the jack cylinder member define a first pressure chamber, and

h. hydraulic fluid supplied to said first pressure chamber urges the pin cylinder and the pressure plate toward the mine roof to clamp the machine between the mine'roof and the mine roof in an incipient pin driving condition.

4. A machine for driving mine roof pins as defined in claim 3, in which:

i. the pin piston and the pin cylinder define a second pressure chamber, and

j. hydraulic fluid supplied to said second pressure chamber urges the pin piston toward the mine roof to drive said pin into said roof.

5. A machine for driving mine roof pins as defined in claim 2, in which:

g. the jack piston member and the jack cylinder member define a first pressure chamber,

h. fluid supplied to said first pressure chamber urges the pin cylinder and the pressure plate toward the mine roof to clamp the machine between the mine roof and the mine floor in an incipient pin driving condition,

i. the pin piston and the pin cylinder define a second pressure chamber,

j. fluid supplied to said second pressure chamber urges the pin piston toward the mine roof to drive said pin into said roof, and

. k. valve means between said first and second chambers controls the fluid flow from first chamber to said second chamber permitting fluid flow between said chambers when pressure in said first chamber is at a predetermined value.

6. A machine for driving mine roof pins as defined in claim 5, in which:

l. the valve means between said first and second chambers permits fluid flow from said second chamber to said first chamber when the pressure in said second chamber is at a predetermined value to permit retraction of the pin piston into the pin cylinder.

7. A machine for driving mine roof pins as defined in claim 6, in which:

m. spacer means between said pin cylinder and said jack cylinder member axially spaces said pin cylinder from said jack cylinder member when the pin cylinder is fully retracted.

8. A machine for driving mine roof pins as defined in claim 6, in which:

n. the valve means includes a concentric valve block integral with the pin cylinder and providing an axial spacer between said pin cylinder and said jack cylinder member.

9. A machine for driving mine roof pins as defined in claim 1, in which:

f. bracket means extending between the pin cylinder and the pressure plate connects said pressure plate to the pin cylinder for movement of the pressure plate in unison with said pin cylinder.

10. In a machine for driving mine roof pins:

a. an elongate pin cylinder,

b. a pin piston movably received in the pin cylinder. the pin piston providing a seat for a mine roof pin,

c. a pin-centering support means extending along the f. a jack cylinder, supported by the base and receiving the pin cylinder in coaxial, telescopic relation, said jack cylinder including a port supplying hydraulic fluid to said jack cylinder for extending the pin cylinder and urging the pressure plate toward the mine roof.

1]. A machine for driving mine roof pins as defined in claim 10, in which:

g. valve means is provided between the piston cylinder and the jack cylinder including:

1. a first check valve opening to admit fluid from the jack cylinder to the pin cylinder when the pin cylinder is extended and the pressure plate operatively engages the mine roof and pressure in the jack cylinder reaches a predetermined value following such engagement, to urge said pin piston toward the mine roof to drive said pin into said roof upon continued supply of fluid to the jack cylinder port, and 2. a second check valve opening to discharge fluid from the pin cylinder to the jack cylinder when the pin cylinder is retracted and the pressure in the pin cylinder reaches a predetermined value. 12. A machine for driving mine roof pins as defined in claim 11, in which:

h. said pin-centering support means includes a plurality of support lengths engaging the side of the pin about the pin periphery, each support length including a plurality of interengaging relatively movable support members each support length being operatively connected to the pin piston members,

i. receiving cylinders, operatively attached to and moving with the pin cylinder, receive each support length, each receiving cylinder including a port supplying hydraulic fluid to said receiving cylinder,

j. a receiving piston is movably mounted in each receiving cylinder and is operatively connected to an associated support length for urging said support length back into said pin cylinder to retract the pin piston when the pressure in the receiving cylinder is sufficient to open the second check valve. 

1. In a machine for driving mine roof pins: a. an elongate pin cylinder, b. a pin piston movably received in the pin cylinder, the pin piston providing a seat for a mine roof pin, c. a pressure plate carried by and movable with the pin cylinder, d. a base supported by the mine floor, and e. jacking means supported by the base and urging the pin cylinder and the pressure plate toward the mine roof, said jacking means including a jack piston member and a jack cylinder member coaxial with the pin cylinder, said jack piston member being integral with said pin cylinder for movement with said pin cylinder and said jack cylinder member being movable relative to said pin cylinder.
 2. A machine for driving mine roof pins as defined in claim 1, in which: f. the jack piston member is telescopically received within the jack cylinder member.
 2. a second check valve opening to discharge fluid from the pin cylinder to the jack cylinder when the pin cylinder is retracted and the pressure in the pin cylinder reaches a predetermined value.
 3. A machine for driving mine roof pins as defined in claim 2, in which: g. the jack piston member and the jack cylinder member define a first pressure chamber, and h. hydraulic fluid supplied to said first pressure chamber urges the pin cylinder and the pressure plate toward the mine roof to clamp the machine between the mine roof and the mine roof in an incipient pin driving condition.
 4. A machine for driving mine roof pins as defined in claim 3, in which: i. the pin piston and the pin cylinder define a second pressure chamber, and j. hydraulic fluid supplied to said second pressure chamber urges the pin piston toward the mine roof to drive said pin into said roof.
 5. A machine for driving mine roof pins as defined in claim 2, in which: g. the jack piston member and the jack cylinder member define a first pressure chamber, h. fluid supplied to said first pressure chamber urges the pin cylinder and the pressure plate toward the mine roof to clamp the machine between the mine roof and the mine floor in an incipient pin driving condition, i. the pin piston and the pin cylinder define a second pressure chamber, j. fluid supplied to said second pressure chamber urges the pin piston toward the mine roof to drive said pin into said roof, and k. valve means between said first and second chambers controls the fluid flow from first chamber to said second chamber permitting fluid flow between said chambers when pressure in said first chamber is at a predetermined value.
 6. A machine for driving mine roof pins as defined in claim 5, in which: l. the valve means between said first and second chambers permits fluid flow from said second chamber to said first chamber when the pressure in said second chamber is at a predetermined value to permit retraction of the pin piston into the pin cylinder.
 7. A machine for driving mine roof pins as defined in claim 6, in which: m. spacer means between said pin cylinder and said jack cylinder member axially spaces said pin cylinder from said jack cylinder member when the pin cylinder is fully retracted.
 8. A machine for driving mine roof pins as defined in claim 6, in which: n. the valve means includes a concentric valve block integral with the pin cylinder and providing an axial spacer between said pin cylinder and said jack cylinder member.
 9. A machine for driving mine roof pins as defined in claim 1, in which: f. bracket means extending between the pin cylinder and the pressure plate connects said pressure plate to the pin cylinder for movement of the pressure plate in unison with said pin cylinder.
 10. In a machine for driving mine roof pins: a. an elongate pin cylinder, b. a pin piston movably received in the pin cylinder, the pin piston providing a seat for a mine roof pIn, c. a pin-centering support means extending along the pin cylinder and moving with the pin piston when the pin piston drives the pin along and out of the pin cylinder and into the mine roof, the pin-centering support means engaging the pin to guide and support the pin as the pin is driven, and moving laterally out of the cylinder as it disengages from that portion of the pin about to enter the mine roof, d. a pressure plate carried by and movable with the pin cylinder, e. a base engageable with the mine roof floor, and f. a jack cylinder, supported by the base and receiving the pin cylinder in coaxial, telescopic relation, said jack cylinder including a port supplying hydraulic fluid to said jack cylinder for extending the pin cylinder and urging the pressure plate toward the mine roof.
 11. A machine for driving mine roof pins as defined in claim 10, in which: g. valve means is provided between the piston cylinder and the jack cylinder including:
 12. A machine for driving mine roof pins as defined in claim 11, in which: h. said pin-centering support means includes a plurality of support lengths engaging the side of the pin about the pin periphery, each support length including a plurality of interengaging relatively movable support members each support length being operatively connected to the pin piston members, i. receiving cylinders, operatively attached to and moving with the pin cylinder, receive each support length, each receiving cylinder including a port supplying hydraulic fluid to said receiving cylinder, j. a receiving piston is movably mounted in each receiving cylinder and is operatively connected to an associated support length for urging said support length back into said pin cylinder to retract the pin piston when the pressure in the receiving cylinder is sufficient to open the second check valve. 